Electrical products having complex electrical circuits, particularly digital systems, require extensive testing to assure proper performance and reliability. Specialized testers, sometimes referred to as test controllers, are normally employed to test the unit's electrical circuits. Such testers may employ a computer-based system having test sofware or test firmware programmed to perform various types of tests on the circuits. The test software or firmware is sometimes referred to as the fault detection/fault location (FD/FL) diagnostics.
In the past, verification of the FD/FL diagnostics has been performed by manually introducing electrical fault signals into the unit under test, and then verifying that the FD/FL properly identifies or records such faults. This manual approach suffers from several deficiencies. First, manual insertion of the faults requires the presence of an operator, is time consuming and quite slow. Manual fault insertion is also particularly subject to human error if an improper fault signal is inserted and may also subject sensitive circuits to damage if the applied current levels are too high. Moreover, the hand-held equipment sometimes used to insert the fault can lack the drive current to pull strong signals to faulty logic states, thereby resulting in invalid fault codes. Finally, it was difficult to correlate performance of the FD/FL executed by the test controller with the particular circuits being tested. Fault data, for example, was often erroneously manually transcribed. As a result of these deficiencies, fault insertion for the purpose of verification of the FD/FL was sometimes given a low priority, or incomplete verification was performed, or was not employed at all, thereby compromising the reliability of the FD/FL test diagnostics.